Powder injection molding binder, powder injection molding composition and method for production of sintered member

ABSTRACT

An injection molding binder permitting formation of a molded article incapable of sustaining such defects as a crack or an expansion at the degreasing step and allowing the degreasing treatment to be completed quickly, an injection molding composition, and a method for the production of a sintered member are disclosed. The powder injection molding binder contains a polymer (I) which is obtained by polymerizing a monomer component composed of 50 to 100% by weight of a long side chain-containing monomer and 0 to 50% by weight of other polymerizable monomer. The powder injection molding composition comprises the binder, a binder auxiliary, and a powdery material capable of sintering. The method for the production of a sintered member comprises the steps of injection molding the composition, subjecting the molded mass to a degreasing treatment, and sintering the degreased molded mass.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a powder injection molding binder, a powderinjection molding composition, and a method for the production of thesintered member in the production of a sintered member from a powderymaterial of metal, ceramic, cermet, or the like by the injection moldingtechnique.

2. Description of the Prior Art

It is well known that injection molding is utilized as a method for theformation of complicatedly molded products of ceramic and metallicsubstances. The injection molding method obtains a sintered member as aproduct by adding to a powdery material various organic compounds and athermoplastic resin for the purpose of imparting fluidity to the powderymaterial, heating and kneading the resultant mixture, injection moldingthe blend in a prescribed shape, degreasing the molded mass, andsintering the shaped mass.

Generally as a binder component, such low molecular compounds asparaffin wax and carnauba wax are prevalently used. Since thesecompounds are deficient in viscosity and in fluidity as well, they arenot easily kneaded with the powdery material, other binder, or the likein the preparation of a powder injection molding composition. Theydeserve no designation of thorough formability because they have theproblem of entraining such detriments as jetting and weld in the processof injection molding. For this reason, the practice of incorporating aplasticizer in this blend for the sake of adjusting the fluidity of theblend has been generally in vogue. The plasticizer, however, oftensuccumbs to decomposition as at the sprue runner part of the moldingdevice and the powder injection molding composition, therefore, is noteasily reclaimed for reuse.

The most important part of a process for the production of a flawlesssintered member resides in the step of degreasing. The degreasing methodwhich is currently in popular use is known in two kinds; the thermaldecomposition method which comprises heating an injection molded massthereby melt-flowing, thermally decomposing and gasifying an organicbinder contained therein and the solvent extraction method whichcomprises treating an injection molded mass with an organic solventthereby expelling an organic binder from the injection molded mass.

According to the degreasing method which removes an organic binder byheating, a desire to defat a molded mass without leaving a defect behindinside the molded mass necessitates the fulfillment of the requirementthat the organic binder is not melt-flowed, thermally decomposed andevaporated concentrically in a short span of time. When the melt-flowingthe thermal decomposition and the evaporation of the organic binder areconcentrated in the short span of time, the interior of the molded massis exposed to pressure, a cause for such damage as a crack and anexpansion. For the purpose of preventing the molded mass from sustaininga crack or an expansion while receiving a degreasing treatment, it isnecessary that the degreasing treatment be allowed to proceed slowlyenough for the organic binder to be thermally decomposed and evaporatedgradually. Particularly when the powdery material is given a decreasedparticle diameter and an increased specific surface area so as to bethermally fluidified stably in the process of injection molding, theamount of the organic binder to be used therein increases and theheating step in the degreasing process necessitates a device such as fordividing the heating step into a multiplicity of stages. The degreasingtreatment, therefore, inevitably consumes a long time. At present, thefeasibility of an idea of adding a subliming substance to the binder isbeing studied. It is likely that the subliming substance in the blendevaporates during the steps of blending and molding. During the moldingstep, the sprue runner part is not easily regenerated.

Then, in the case of the method which expels the organic binder from theinjection molded mass by the use of an organic solvent, the component ofthe organic binder which is soluble in the solvent is dissolved out ofthe molded mass by the solvent and the portions of the organic binderconsequently removed form passageways, with the result that the rest ofthe organic binder will be thermally decomposed and evaporated smoothly.The molded mass, therefore, sustains such damage as a crack or anexpansion with great difficulty during the degreasing step. Since thesolvent extraction method which is currently prevalent uses a largeamount of such a liquid raw material as mineral oil, fatty acid typeoil, or natural oil as an organic binder, the injection molded massoften entrains exudation of the oil therefrom. Even during theprotracted storage of the raw materials prepared for the production ofthe injection molded mass, the exudation of the oil disrupts thestability of storage of the raw materials. When the injection moldedmass is stored for a long time, it often happens that the oil which hasexuded to the surface induces the molded mass to sustain a crack or anexpansion during the steps of extraction and degreasing.

An invention which contemplates using a water-soluble resin as a binderand extracting this water-soluble resin from the molded mass by the useof water is disclosed in JP-A-02-101,101, for example. Owing to the useof water for degreasing, this invention is at an advantage in attainingthe degreasing treatment less expensively and more safely. The waternevertheless has the drawback of exhibiting poor penetrating power tothe injection molded mass and attaining slow evaporation therefrom ascompared with a solvent. Particularly when a cermet powder having aspecific surface area of about 10 m² /g and requiring use of a largeamount of an organic binder is used, the drying treatment to beperformed after the extracting treatment consumes a long time. When thewater which has permeated the molded mass deeply to the core is to beremoved by heating, the molded mass possibly sustains a crack or anexpansion as the temperature of heating is elevated. Since water is usedfor degreasing the molded mass, the powder of iron, copper, or the likewhich gathers rust on contact with water cannot be used for theinvention under consideration. Then, the ceramic substance such as, forexample, Si₃ N₄ has the problem of emitting ammonia gas on reacting withwater and, therefore, imposing a limit on the raw materials to be usedfor the production of a molded article.

An object of this invention, therefore, is to provide a novel powderinjection molding binder, a powder injection molding composition, and amethod for the production of a sintered member.

Another object of this invention is to provide an injection moldingbinder which exhibits a highly desirable kneading property during themanufacture of a powder injection molding composition even in theabsence of a plasticizer and avoids incurring such detriments as jettingor weld during the injection molding and an injection moldingcomposition.

Still another object of this invention is to provide an injectionmolding binder which permits formation of a molded article incapable ofsustaining such defects as a crack or an expansion at the degreasingstep and allows the degreasing treatment to be completed quickly, aninjection molding composition, and a method for the production of asintered member.

A further object of this invention is to provide an injection moldingcomposition which allows formation of a stable injection molded articleincurring no exudation of oil therefrom even during a protractedstorage.

SUMMARY OF THE INVENTION

The various objects mentioned above are accomplished by a powderinjection molding binder containing a polymer (I) obtained bypolymerizable a monomer component comprising 50 to 100% by weight of atleast one long side chain-containing monomer selected from the groupconsisting of long side chain-containing vinyl monomers represented bythe formula I: ##STR1## wherein R¹ is H or CH₃, R² is an aliphatichydrocarbon group having from 15 to 30 carbon atoms, and B is ##STR2##wherein R³ is a divalent organic group, or ##STR3## and long sidechain-containing maleic monomers represented by the formula II: ##STR4##wherein R⁴ and R⁵ are independently H or an aliphatic hydrocarbon grouphaving from 1 to 30 carbon atoms, providing at least either of R⁴ and R⁵is an aliphatic hydrocarbon group having from 15 to 30 carbon atoms, andfrom 50 to 0% by weight of other polymerizable monomer.

The objects are also accomplished by a powder injection moldingcomposition comprising (a) from 20 to 80% by volume of a powderymaterial capable of sintering, (b) from 10 to 70% by volume of a polymer(I) obtained by polymerizing a monomer component comprising from 50 to100% by weight of at least one long chain-containing monomer selectedfrom the group consisting of long side chain-containing vinyl monomersrepresented by the formula I and long side chain-containing maleicmonomers represented by the formula II and from 50 to 0% by weight ofother polymerizable monomer, and (c) from 10 to 70% by volume of abinder auxiliary (II) (providing the total of the powdery material, thepolymer (I), and the binder auxiliary (II) accounts for 100% by volume).

The objects are further accomplished by a powder injection moldingcomposition comprising a powdery material capable of sintering, from 10to 90% by weight of the polymer (I), and from 90 to 10% by weight of thebinder auxiliary (II).

The objects are further accomplished by a method for the production of asintered member, comprising the steps of subjecting the powder injectionmolding composition mentioned above to an injection molding treatmentthereby obtaining a molded mass, subjecting the resultant molded mass toa degreasing treatment thereby extracting the binder component from themolded mass, and further subjecting the defatted shaped mass to asintering treatment.

The objects are further accomplished by a method for the production of asintered member, comprising the steps of subjecting a powder injectionmolding composition comprising a powdery material capable of sintering,from 10 to 90% by weight of the polymer (I), and from 90 to 10% byweight of the binder auxiliary (II) to an injection molding treatment,subjecting the resultant molded mass to a degreasing treatment, andfurther subjecting the defatted shaped mass to a sintering treatment.

The powder injection molding binder of this invention allows a powderymaterial capable of sintering to be injection molded with highformability and imparts a highly desirable degreasing property to theinjection molded mass. The effects of the powder injection moldingbinder will be more specifically enumerated below.

Since the binder has highly desirable affinity for metals, ceramics, andcermets, it uniformly permeates the powdery material at the step ofkneading.

Since the binder has highly desirable viscosity, the blended massexhibits highly desirable fluidity at the step of injection molding evenin the absence of a plasticizer.

Since the binder obviates the necessity for using a plasticizer as anadditive, it imparts an excellent recycling property to the powderinjection molding composition.

Since the binder possesses viscosity and molecular weight in a finestate of balance, the blended mass does not incur such defects asjetting and weld during the injection molding treatment.

Since the binder shows markedly high solubility to an organic solvent,the injection molded mass is defatted quickly to an ideal extent at thedegreasing treatment using an organic solvent. Further, the solventneither swells the shaped mass nor consequently disintegrates it at thedegreasing step.

Owing to these features, sintered members having highly complicatedshapes including thin-wall shapes can be produced efficiently even on aquantity basis.

EXPLANATION OF THE PREFERRED EMBODIMENT

The aforementioned polymer (I) which is an essential component for theconstruction of the powder injection molding binder of this invention isobtained by polymerizing a monomer component comprising from 50 to 100%by weight, preferably from 80 to 100% by weight, of at least one longside chain-containing monomer (A) selected from the group consisting oflong side chain-containing monomers (A-1) and (A-2) representedrespectively by the formulas I and II mentioned above and from 50 to 0%by weight, preferably from 20 to 0% by weight, of other polymerizablemonomer (B) (providing the total of the long chain-containing monomer(A) and the other monomer (B) accounts for 100% by weight). If theamount of the long side chain-containing monomer (A) is less than thelower limit of the range mentioned above, the powder injection moldingbinder will suffer degradation of crystallinity and solubility andconsume unduly long time at the degreasing step. In the monomercomponent, when the total amount of the long side chain-containingmonomers (A) represented by the formula I and the formula II is not lessthan 50% by weight and less than 100% by weight, the polymerizablemonomer (B) other than long side chain-containing vinyl monomers (A-1)and long side chain-containing maleic monomers (A-2) which will bespecifically described hereinbelow accounts for the rest of the monomercomponent.

When a long side chain-containing maleic monomer (A-2) is used as thelong side chain-containing monomer (A), the amount of the long sidechain-containing maleic monomer is preferable to be in the range of from50 to 80% by weight, preferably from 50 to 60% by weight and the rest ofthe monomer component is preferable to be a long side chain-containingvinyl monomer (A-1) and/or other monomer (B) providing the amount of theother monomer (B) is in the range of from 50 to 0% by weight, preferablyfrom 20 to 0% by weight. As the long side chain-containing monomer (A),the long side chain-containing vinyl monomer (A-1) is preferably 30 to50% by weight!.

The melt viscosity of the polymer (I) at 80° to 180° C. is preferable tobe in the range of from 50 to 7000 cps, preferably from 500 to 3000 cps.If the melt viscosity is less than 50 cps, the blend will incur jettingat the injection molding step. If it exceeds 7000 cps, the possibilityarises that the wetting property of the powdery material will be loweredand the strength of the sintered member will be decreased, theworkability of the blend at the injection molding step will be impaired,the molded mass will sustain a crack or an expansion at the degreasingstep, and the degreasing treatment will consume an unduly long time. Thesoftening temperature of the polymer (I) is preferable to be in therange of from 30° to 100° C., preferably from 40° to 60° C. If thistemperature is less than 30° C., the molded mass will be disintegratedat the degreasing step. If it exceeds 100° C., the molded mass willsustain a crack or an expansion and the degreasing treatment willconsume an unduly long time. The weight average molecular weight of thepolymer (I) is desired to be in the range of from 1,000 to 500,000,preferably from 10,000 to 70,000. If this molecular weight deviates fromthe range mentioned above, the molded mass will sustain a crack or anexpansion and the degreasing treatment will consume an unduly long time.

Now, the method for producing the polymer (I) to be used in thisinvention will be described. This polymer is obtained by polymerizing amonomer component comprising 50 to 100% weight of at least one long sidechain-containing monomer selected from the group consisting of long sidechain-containing vinyl monomers represented by the formula I: ##STR5##wherein R¹ is H or CH₃, preferably H, R² is an aliphatic hydrocarbongroup having from 15 to 30 carbon atoms, and B is ##STR6## wherein R³ isa divalent organic group, or ##STR7## and long side chain-containingmaleic monomers represented by the formula II: ##STR8## wherein R⁴ andR⁵ are independently H or an aliphatic hydrocarbon group having from 1to 30 carbon atoms, preferably an aliphatic hydrocarbon group havingfrom 15 to 30 carbon atoms, providing at least either, preferably both,of R⁴ and R⁵ are an aliphatic hydrocarbon group having from 15 to 30carbon atoms, and from 50 to 0% by weight of other polymerizablemonomer.

The polymerization can be carried out in the form of radicalpolymerization, ionic polymerization, or the like. As respects themethod of polymerization, all the polymerization methods such as bulkpolymerization, solution polymerization, emulsion polymerization, andsuspension polymerization can be adopted. The polymer (I) is obtained inthe form of a solution or a solid having the polymer (I) dissolvedtherein, a suspension liquid having solid particles of the polymer (I)dispersed in a medium, or an emulsion having solution particles of thepolymer (I) dispersed in a medium. The polymer (I) is obtained in asolid state by removing the unaltered monomer and the solvent and othervolatile components from the reaction mixtures mentioned above. Thepolymer (I) can be manufactured in all forms such as block, graft, andrandom polymerization.

As typical examples of the long side chain-containing vinyl type monomer(A-1), higher alkyl esters of (meth)acrylic acids which are the estersof (meth)acrylic acids with higher alcohols of from 15 to 30 carbonatoms such as stearyl (meth)acrylates, behenyl (meth)acrylates,n-pentadecyl (meth)acrylates, palmityl (meth)acrylates, n-nonadecyl(meth)acrylates, eicosyl (meth)-acrylates, ceryl (meth)acrylates, oleyl(meth)acrylates, and eicosenyl (meth)acrylates; adducts of suchmonobasic straight chain fatty acids as stearic acid with suchpolymerizing monomers as glycidyl (meth)acrylates and isopropenyloxazoline which are capable of addition reaction with a carboxyl group;adducts of such higher alcohols as stearyl alcohol and oleyl alcoholwith polyisocyanate compounds and such hydroxyl group-containingpolymerizing monomers as hydroxyethyl (meth)acrylates; and such vinylesters of higher fatty acids as vinyl stearate may be cited.

As typical examples of the long side chain-containing maleic acid typemonomer (A-2), such higher alkyl maleates as mono-stearyl maleate,monobehenyl maleate, mono-n-pentadecyl maleate, monopalmityl maleate,mono-n-nonadecyl maleate, monoeicosyl maleate, monoceryl maleate,monooleyl maleate, monoeicosenyl maleate, distearyl maleate, dibehenylmaleate, di-n-pentadecyl maleate, dipalmityl maleate, di-n-nonadecylmaleate, dieicosyl maleate, diceryl maleate, dioleyl maleate, anddieicosenyl maleate; and such higher alkyl fumarates as monostearylfumarate, monobehenyl fumarate, monopalmityl fumarate, monoeicosylfumarate, monopalmityl fumarate, monoeicosyl fumarate, monocerylfumarate, monooleyl fumarate, monoeicosenyl fumarate, distearylfumarate, dibehenyl fumarate, dipalmityl fumarate, dieicosyl fumarate,dipalmityl fumarate, dieicosyl fumarate, diceryl fumarate, dioleylfumarate, and dieicosenyl fumarate may be cited.

The polymerizable monomer (B) other than the long side chain-containingvinyl monomer (A-1) and the long side chain-containing maleic monomer(A-2) to be used for the synthesis of the polymer (I) has no particularrestriction. Such styrene derivatives as styrene, vinyl toluene,α-methyl styrene, and chloromethyl styrene; such (meth)acrylic esters asmethyl (meth)acrylates, ethyl (meth)acrylates, butyl (meth)acrylates,dodecyl (meth)acrylates, and 2-ethylhexyl (meth)acrylates which aresynthesized by the esterification of (meth)acrylic acids withmonoalcohols of 1 to 14 carbon atoms; such unsaturated carboxylic acidsas (meth)acrylic acids, crotonic acid, maleic acid, fumaric acid, anditaconic acid, or half esters thereof, or salts thereof; such(meth)acrylamide derivatives as (meth)acryl amides, N-monomethyl(meth)acryl amides, N-monoethyl (meth)acryl amides, N,N-dimethyl(meth)acryl amides, N-methylol (meth)acryl amides, and N-butoxymethyl(meth)acryl amides, salts thereof, and quaternary compounds thereof;such hydroxyl group-containing unsaturated monomers as 2-hydroxyethyl(meth)acrylates, 2-hydroxypropyl (meth)acrylates, and monoesters of(meth)acrylic acids with polypropylene glycol or polyethylene glycol;such sulfonic acid group-containing unsaturated monomers as ethyl(meth)acrylic acid-2-sulfonates, vinyl sulfonic acid, styrene sulfonicacid, and salts thereof; such basic unsaturated monomers asdimethylaminoethyl (meth)acrylates, dimethylaminoethyl (meth)-acrylamides, dimethylaminopropyl (meth)acryl amides, vinyl pyridine, vinylimidazole, and vinyl pyrrolidone; such polyfunctional (meth)acrylicesters as esters of (meth)acrylic acids with such polyhydric alcohols asethylene glycol, 1,3-butylene glycol, diethylene glycol, 1,6-hexaneglycol, neopentyl glycol, polyethylene glycol, polypropylene glycol,trimethylol propane, pentaerythritol, and dipentaerythritol which haveat least two polymerizing unsaturated groups in the molecular unitsthereof; such organic silicon group-containing unsaturated monomers asvinyl trimethoxy silane, γ-(meth)acryloylpropyl trimethoxy silane, allyltriethoxy silane, and trimethoxysilyl-propylallyl amine; such oxazolinegroup-containing polymerizing monomers as 2-isopropenyl-2-oxazoline and2-vinyl oxazoline; such epoxy group-containing polymerizing monomers asglycidyl (meth)-acrylates and acrylglycidyl ether; such halogenatedunsaturated monomers as vinyl fluoride, vinylidene fluoride, vinylchloride, and vinylidene chloride; such halohydrin group-containingunsaturated monomers as 2-hydroxy-3-chloropropylene (meth)acrylates;such aziridinyl group-containing polymerizing monomers as2-aziridinylethyl (meth)acrylates; such blocked isocyanategroup-containing unsaturated monomers as reaction adduts of 2-isocyanateethyl (meth)acrylate with ethyl alcohols; such unsaturated monomers asdivinyl benzene and diallyl phthalate which have two ethylenicallyunsaturated groups; such vinyl esters of saturated carboylic acids asvinyl acetate; (meth)-acrylonitriles; and acrolein, for example, areusable. These polymerizing monomers may be used either singly or in theform of a mixture of two or more members.

For the synthesis of the polymer (I), the method of radicalpolymerization using a radical polymerization initiator is adopteddesirably. Any of the well-known radical polymerization initiators ofboth the oil-soluble and the water-soluble type can be used. As typicalexamples of the oil-soluble initiator, such azo compounds asazo-bis-isobutyronitrile, azo-bis-valeronitrile, 2,2¹-azo-bis-(2,4-dimethyl valeronitrile),1,1'-azo-bis-(cyclo-hexane-1-carbonitrile),2,2'-azo-bis-(2-aminopropane) dihydro-chloride, and4,4'-azo-bis-(4-cyanopentanoic acid); and such organic peroxides asbenzoyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, t-butylhydroperoxide, and t-butyl peroxy-2-ethylhexanolate may be cited. Astypical examples of the water-soluble initiator, potassium persulfate,ammonium persulfate, and hydrogen peroxide may be cited. For the purposeof heightening the rate of polymerization, an oxidizing agent typepolymerization initiator may be used, when necessary, as combined with areducing agent so as to function as a redox type initiator. The amountof the polymerization initiator to be used is in the range of from 0.01to 5 parts by weight, preferably from 0.5 to 2 parts by weight, based on100 parts by weight of the polymerizing monomer component. The additionof the radical polymerization initiator can be made at a suitable timeas in the standard radical polymerization. For the radicalpolymerization of the polymerizing monomer component, any of thepolymerization apparatuses heretofore known in the art may be adopted.The polymerization temperature is in the range of from 0° to 200° C.,preferably from 50° to 150° C. The polymerization time is in the rangeof from 1 to 15 hours, preferably from 3 to 8 hours.

The powder injection molding binder of this invention is obtained bymixing the polymer (I) mentioned above with such binder auxiliaries (II)as binding agent, plasticizer, and slip additive, for example.

The binder auxiliary (II) is composed of binding agent, plasticizer,slip additive, or the like which are generally used for powder injectionmolding. As concrete examples of the binding agent, polyethylene,polypropylene, polybutene, poly-styrene, ethylene-vinyl acetatecopolymer, cellulose acetate, polybutyl methacrylate, acrylic resinsexcepting the polymer (I), polyvinyl alcohol, carboxymethyl cellulose,glucose, methyl cellulose, starch, dextrin, molasses, gelatin, spentliquor, peptone, polyvinyl ether, ethyl cellulose, acetyl cellulose,wax, liquid paraffin, heavy oil, machine oil, phenol resin, ethylsilicate, polyacetal, and nylon type resins may be cited. These bindingagents may be used singly or in the form of a mixture of two or moremembers. As typical examples of the slip additive, such waxes asparaffin wax, microcrystalline wax, urethanated wax, and Fischer-Tropschwax, such higher fatty acids as polyethylene glycol and stearic acid,such metallic salts of higher fatty acid as aluminum stearate andmagnesium stearate, such higher fatty acid esters as diglycol stearate,flour, and mineral oil may be cited. These slip additives may be usedsingly or in the form of a mixture of two or more members.

As typical examples of the plasticizer, such aliphatic diesters asdiethyl phthalate, dibutyl phthalate, and dioctyl phthalate andaliphatic monoesters may be cited. These plasticizers may be used singlyor in the form of a mixture of two or more members. Generally, thebinder auxiliary (II) incorporates one species of binding agent and onespecies of slip additive and, where the powder injection moldingcomposition does not need to be recycled, optionally incorporatesadditionally a plasticizer. The powder injection molding binder of thisinvention can be produced by mixing the polymer (I) with the binderauxiliary (II). The mixing ratio in this case is desired to be 10 to 90%by weight of the polymer (I) to 90 to 10% by weight of the binderauxiliary (II), preferably 30 to 80% by weight of the polymer (I) to 70to 20% by weight of the binder auxiliary (II).

The method for mixing the polymer (I) with the binder auxiliary (II) hasno particular restriction. Any of the mixing methods heretofore known tothe art may be adopted. They may be mixed by the use of a kneader at atemperature in the range of from 80° to 200° C., preferably from 100° to170° C., for a period in the range of from 0.5 to 3 hours, preferablyfrom 0.5 to 1 hour.

The powder injection molding composition of this invention is composedof a powdery material capable of sintering and the powder injectionmolding binder mentioned above. To be more specific, it is composed ofthe powdery material capable of sintering, the polymer (I), and thebinding auxiliary (II).

Preferably, an amount of the powdery material capable of sintering is inthe range of from 20 to 80% by volume, that of the polymer (I) in therange of from 10 to 70% by volume, and that of the binder auxiliary (II)in the range of from 10 to 70% by volume. Preferably, the amount of thepowdery material capable of sintering is in the range of from 40 to 70%by volume, that of the polymer (I) in the range of from 10 to 50% byvolume, and that of the binder auxiliary (II) in the range of from 10 to50% by volume. The total of the amounts of the powdery material, thepolymer (I), and the binder auxiliary (II) is 100% by volume.

The method for mixing the powdery material capable of sintering, thepolymer (I), and the binder auxiliary (II) in the production of thepowder injection molding composition of this invention has no particularrestriction. Any of the mixing methods well known in the art may beadopted. They may be mixed by the use of a kneader at a temperature inthe range of from 80° to 200° C., preferably from 100° to 170° C., for aperiod in the range of from 0.5 to 3 hours, preferably from 0.5 to 1hours. It is permissible to adopt instead the method which comprisesmixing the polymer (I) with the binder auxiliary (II) to prepare aninjection molding binder and mixing this binder with the powderymaterial capable of sintering prior to use or the method which comprisesmixing the powdery material capable of sintering with the polymer (I)and the binder auxiliary (II) prior to use.

The powder injection molding composition of this invention, whennecessary, may be pulverized into pellets of a varying particle diameterto be desired.

As typical examples of the powdery material capable of sintering andusable in this invention, such metal powder as metallic silicon powder,iron or iron alloy powder such as high speed steel, super alloy powdersuch as titanium, tungsten or boron-containing alloy, and such ceramicspowder as silicon nitride powder, silicon carbide powder, aluminapowder, zirconia powder, sialon powder(silicon-nitride-alumina) may becited. Further, cermet powder which is a mixture of metal powder andceramics powder may be used, and if necessary, at least one kind ofmetal powder and ceramics powder may be used. The average particlediameter of the powdery material is in the range of from 0.01 to 1,000μm, preferably from 0.1 to 20 μm.

Now, the method of this invention for producing a sintered member fromthe powdery material will be described hereinbelow. The sintered memberis obtained by injection molding the powder injection moldingcomposition of this invention thereby obtaining a molded mass, thensubjecting the molded mass to a degreasing treatment thereby expellingthe binder component from the molded mass, and sintering the defattedmolded mass.

The method for effecting the injection molding is not specificallylimited. Any of the injection molding methods well known in the art maybe adopted. The injection molding can be carried out at a temperature inthe range of from 80° to 200° C., preferably from 160° to 180° C., undera pressure in the range of from 300 to 2,500 kg/cm², preferably from 600to 1,000 kg/cm², for example.

At the degreasing step, the powder injection molding binder is removed.The degreasing treatment is effected by the use of a solvent or by theapplication of heat. In this invention, the procedure which comprisesfirst degreasing the blended mass with a solvent thereby removing thegreater part of the polymer (I) and part of the binder auxiliary (II)and then heating the defatted mass thereby removing the residual organicsubstances proves particularly preferable. As typical examples of theorganic solvent to be used at the degreasing step, chlorine-containingsolvents as methylene chloride, dichloroethane, trichloroethane, andcarbon tetrachloride; aromatic solvents such as benzene, toluene, andxylene; aliphatic type solvents such as hexane, heptane, cyclohexane,decalin, tetralin, and petroleum ether; alcohol type solvents such asmethanol, ethanol, propanol, butanol, hexanol, butyl cellosolve, andbutyl carbitol; ketone type solvents such as acetone and methylethylketone; nitrogen containing type solvents such as dimethyl formamide,nitromethane and acetonitrile; ester type solvents such as ethyl acetateand butyl acetate; sulfur-containing type solvents such as dimethylsulfoxide and carbon disulfide; and complex type solvents such asethanol amine may be cited. These solvents may be used singly or in theform of a mixture of two or more members.

The degreasing treatment is preferable to be carried out at atemperature in the range of from 20° to 80° C. for a period in the rangeof from 10 to 360 minutes, preferably at a temperature in the range offrom 20° to 40° C. for a period in the range of from 30 to 180 minutes.If necessary, stirring the solvent may promote the degreasing. Thedegreasing treatment by the use of the solvent is preferable to removefrom 70 to 90% of the powder injection molding binder of this invention.Then, the residual binder is removed by heating in a degreasing furnaceunder an atmosphere of normal pressure, decreased pressure, or vacuum.The conditions for this degreasing treatment are not particularlylimited. The treatment may be carried out under an atmosphere ofnitrogen gas at a temperature increasing rate of 30° to 100° C. per hourfrom room temperature to 500° C.

The sintered member aimed at by this invention is obtained by sinteringthe molded mass which results from the degreasing treatment. Theconditions for the sintering treatment may be those which are generallyadopted for any sintering process. For example, the sintering treatmentis accomplished by holding the shaped mass under a vacuum or in anatmosphere of inert gas at 1300° C. for 2 hours.

Now, working examples of this invention and controls will be citedbelow. It should be noted that this invention is not limited to theworking examples.

REFERENTIAL EXAMPLE 1

In a flask provided with a dropping funnel, a stirrer, a nitrogen inlettube, a thermometer, and a condenser, 100 parts of toluene was gentlystirred and heated to 80° C. as swept with nitrogen gas. Then, apolymerizing monomer solution prepared in advance by mixing 100 parts ofstearyl acrylate with 200 parts of toluene and 1 part of2,2'-azo-bis-isobutyronitrile was added dropwise through the droppingfunnel to the heated toluene over a period of 2 hours and leftpolymerizing therein at 80° C. After the dropwise addition wascompleted, the reaction solution was kept at the same temperature for 1hour and then left aging in a refluxed state for 2 hours. Consequently,a toluene solution having a solids content of 25.2% was obtained. Whenthis solution was analyzed by gas chromatography, no residual monomerwas detected. This fact indicates that the conversion was 100%. Thissolution was heated under a reduced pressure to expel toluene and obtaina white solid compound (a-1) having a weight average molecular weight of6,000.

REFERENTIAL EXAMPLE 2

In the same flask as used in Referential Example 1, 33 parts of toluenewasgently stirred and heated to 80° C. as swept with nitrogen gas. Then,a polymerizable monomer solution prepared in advance by mixing 100 partsof stearyl methacrylate with 33 parts of toluene and 0.4 part of2,2'-azo-bis-isobutyronitrile was added dropwise through the droppingfunnel into the heated toluene over a period of 2 hours and leftpolymerizing therein at 8° C. After the dropwise addition was completed,the reaction solution was kept at the same temperature for 1 hour andthen left aging in a refluxed state for 2 hours. Consequently, a toluenesolution having a solids content of 60.0% was obtained. When thissolution was analyzed, the conversion was found to be 100%. Thissolution was heated under a reduced pressure to expel toluene and obtaina white solid compound (a-2) having a weight average molecular weight of47,000.

REFERENTIAL EXAMPLE 3

In the same flask as used in Referential Example 1, 33 parts of toluenewasgently stirred and heated to 80° C. as swept with nitrogen gas. Then,a polymerizable monomer solution prepared in advance by mixing 80 partsof stearyl acrylate with 15 parts of behenyl acrylate, 5 parts ofstyrene, 33 parts of toluene, and 0.4 part of2,2'-azo-bis-isobutyronitrile was added dropwise through the droppingfunnel into the heated toluene over a period of 2 hours and leftpolymerizing therein at 80° C. After the dropwise addition wascompleted, the reaction solution was kept at the same temperature for 1hour and then left aging in a refluxed state for 2 hours. Consequently,a toluene solution having a solids content of 60.2% was obtained. Whenthis solution was analyzed, the conversion was found to be 100%. Thissolution was heated under a reduced pressure to expel toluene and obtaina white solid compound (a-3) having a weight average molecular weight of50,000.

REFERENTIAL EXAMPLE 4

In the same flask as used in Referential Example 1, 33 parts of toluenewasgently stirred and heated to 80° C. as swept with nitrogen gas. Then,a polymerizable monomer solution prepared in advance by mixing 80 partsof stearyl acrylate with 15 parts of stearyl maleate, 5 parts ofstyrene, 33 parts of toluene, and 0.4 part of2,2'-azo-bis-isobutyronitrile was added dropwise through the droppingfunnel into the heated toluene over a period of 2 hours and leftpolymerizing therein at 80° C. After the dropwise addition wascompleted, the reaction solution was kept at the same temperature for 1hour and then left aging in a refluxed state for 2 hours. Consequently,a toluene solution having a solids content of 60.0% was obtained. Whenthis solution was analyzed, the conversion was found to be 100%. Thissolution was heated under a reduced pressure to expel toluene and obtaina white solid compound (a-4) having a weight average molecular weight of42,000.

COMPARATIVE REFERENTIAL EXAMPLE 1

In the same flask as used in Referential Example 1, 33 parts of toluenewasgently stirred and heated to 80° C. as swept with nitrogen gas. Then,a polymerizable monomer solution prepared in advance by mixing 40 partsof stearyl acrylate with 60 parts of styrene, 33 parts of toluene, and0.4 part of 2,2'-azo-bis-isobutyronitrile was added dropwise through thedropping funnel into the heated toluene over a period of 2 hours andleft polymerizing therein at 80° C. After the dropwise additionwascompleted, the reaction solution was left aging at the sametemperature for1 hour and then combined with an initiator solutioncomposed of 0.2 part of2,2'-azo-bis-isobutyronitrile and 4 parts oftoluene. Then, the resultant mixture was left aging under a refluxedstate for 2 hours. Consequently, atoluene solution having a solidscontent of 60.0% was obtained. When this solution was analyzed, it wasfound to contain 0.4% of styrene. This fact indicates that theconversion was 99.6%. This solution was heated under a reduced pressureto expel toluene and obtain a white solid compound (b-1) having a weightaverage molecular weight of 68,000.

EXAMPLES 1 AND 2

Powder injection molding binders (1) and (2) were obtained by kneadingthe following sets of components at 140° C. for 40 minutes.

Powder injection molding binder (1)

30 parts by weight of compound (a-1), 40 parts by weight ofpolypropylene, and 30 parts by weight of paraffin wax.

Powder injection molding binder (2)

30 parts by weight of compound (a-2), 30 parts by weight ofpolyethylene, and 20 parts by weight of paraffin wax.

EXAMPLES 3 THROUGH 6

Powder injection molding compositions (1) and (4) were obtained bykneadingthe following sets of components by the use of a pressurekneader at 140° C. for 40 minutes, extracting the mixtures from thekneader, and pulverizing the mixtures.

Powder injection molding composition (1)

60% by volume of powdered stainless steel (a) and 40% by volume ofpowder injection molding binder (1).

Powder injection molding composition (2)

55% by volume of iron-nickel 36% powder and 45% by volume of powderinjection molding binder (2).

Powder injection molding composition (3)

50% by volume of nitrogenated silicon, 18% by volume of polyethylene,18% by volume of paraffin wax, and 14% by volume of compound (a-3).

Powder injection molding composition (4)

50% by volume of powdered stainless steel (b), 18% by volume ofpolypropylene, 14% by volume of paraffin wax, and 18% by volume ofcompound (a-4).

Note) Powdered stainless steel (a): Product of Mitsubishi Steel Mfg.Co., Ltd. (average particle diameter 6 μm).

Iron-nickel 36% powder: Product of Taiheiyo Metal Co., Ltd. (averageparticle diameter 10 μm).

Nitrogenated silicon powder: Product of Ube Industries, Co., Ltd.(average particle diameter 0.5 μm).

Polyethylene: Product of Tokuyama Soda Co., Ltd., PN-670.

Paraffin wax: Product of Nippon Seiro Co., Ltd., SP0145.

Powdered stainless steel (b): Product of Taiheiyo Metal Co., Ltd.(average particle diameter 8 μm).

Polypropylene: Product of Tokuyama Soda Co., Ltd., PN670.

Controls 1 through 3

Powder injection molding compositions for comparison (1) through (3)were obtained by kneading the following sets of component by the use ofa pressure kneader at 140° C. for 40 minutes, extracting the resultantmixtures from the kneader, and pulverizing the mixtures.

Powder injection molding composition for comparison (1)

50% by volume of powdered stainless steel (b), 18% by volume ofpolypropylene, 14% by volume of paraffin wax, and 18% by volume ofcompound (b-1).

Powder injection molding composition for comparison (2)

50% by volume of nitrogenated silicon, 18% by volume of polyethylene,18% by weight of paraffin wax, and 14% by volume of carnauba wax.

Powder injection molding composition for comparison (3)

50% by volume of powdered stainless steel (b), 18% by volume ofpolypropylene, 14% by volume of paraffin wax, and 18% by volume ofpeanut oil.

Note) Peanut oil: Product of Nakaraichisuku (reagent). Carnauba wax:Product of Kishida Chemical (reagent).

EXAMPLE 7

Samples of the powder injection molding compositions (1) through (4)obtained in Examples 3 through 6 were each injection molded at a moldingtemperature of 150° C. under an injection pressure of 1800 kg/cm² toobtain molded pieces (1) through (4) 4 mm in thickness, 10 mm in width,and 50 mm in length. These molded pieces were stored at room temperaturefor 7 days and visually examined. Then, the molded pieces werekeptimmersed in 50 ml of xylene or decalin for 180 minutes and then dried toobtain extracted shaped pieces (1) through (4). The extracts wereanalyzed to define the ratios of extraction of binder. The results areshown in Table 1. The ratio of extraction was calculated in accordancewith the formula: Ratio of extraction=(Weight of extractedbinder)÷(Total weight of binder). It has been demonstrated that themolded pieces using the powder injection molding binder and the powderinjection molding composition according to this invention did notsustain such damage as a crack or an expansion at the degreasing stepand produceshigh ratios of extraction.

                  TABLE 1                                                         ______________________________________                                                               Ratio of                                                                      extraction (%)                                                 Appearance after 7 days' standing                                                              Xylene  Decalin                                      ______________________________________                                        Molded piece (1)                                                                        No abnormal sign observed                                                                        35      32                                       Molded piece (2)                                                                        No abnormal sign observed                                                                        32      31                                       Molded piece (3)                                                                        No abnormal sign observed                                                                        34      32                                       Molded piece (4)                                                                        No abnormal sign observed                                                                        33      32                                       ______________________________________                                    

Control 4

Samples of the powder injection molding compositions for comparison (1)through (3) obtained in Control 1 through 3 were each injection moldedto obtain molded pieces for comparison (1) through (3) by the procedureof Example 7.

The molded pieces for comparison (1) through (3) were tested for ratioof extraction by following the procedure of Example 7. The results areshown in Table 2. The molded pieces for comparison (1) and (2) werefound to show low ratios of extraction and sustain damage due to a crackor expansion. The molded piece for comparison (3), after 7 days'standing at room temperature, showed a sign of oil exudation on thesurface.

                  TABLE 2                                                         ______________________________________                                                                 Ratio of                                                           Appearance after                                                                         extraction (%)                                                     7 days' standing                                                                         Xylene  Decalin                                      ______________________________________                                        Molded piece for comparison (1)                                                               No abnormal  Rupture 8                                        Molded piece for comparison (2)                                                               No abnormal  10      5                                        Molded piece for comparison (3)                                                               Exudation of oil                                                                           35      30                                                       observed                                                      ______________________________________                                    

EXAMPLE 8

The extracted shaped pieces (1) through (4) obtained in Example 7 weresintered in the air at 320° C. to obtain sintered members (1) through(4). The sintered members were tested for relative density. The resultsare shown in Table 3. The relative density was calculated in accordancewith the formula: Relative density=(Found density)÷(Calculated density).It has been demonstrated that the sintered members obtained from thepowder injection molding compositions using the powder injection moldingbinders of this invention possessed very high degrees of relativedensity.

                  TABLE 3                                                         ______________________________________                                                      Relative density                                                ______________________________________                                        Sintered member (1)                                                                           96.0                                                          Sintered member (2)                                                                           97.2                                                          Sintered member (3)                                                                           98.1                                                          Sintered member (4)                                                                           96.7                                                          ______________________________________                                    

What is claimed is:
 1. A powder injection molding composition comprising(a) from 20 to 80% by volume of a powdery material capable of sintering,(b) from 10 to 70% by volume of an organic solvent soluble polymer (I)obtained by polymerizing a monomer component comprising from 50 to 100%by weight of at least one long side chain-containing monomer selectedfrom the group consisting of(i) long side chain-containing vinylmonomers represented by the formula (1)

    CH.sub.2 ═C(R.sup.1)--B--R.sup.2                       ( 1)

wherein R¹ is H or CH₃, R² is an aliphatic hydrocarbon group having from15-30 carbon atoms and B is --C(O)--O--, --C(O)NH.CH₂.CH₂.O.C(O)--,--C(O)NH.CH(OH).CH₂.O.C(O)--, or--C(O)NH.CH₂.CH₂.O.C(O)NH.R³.NH.C(O)O--wherein R³ is a divalent organicgroup or --O.C(O)--, and (ii) long side chain-containing maleic monomersrepresented by the formula (2) ##STR9## wherein R⁴ is H or an aliphatichydrocarbon group having from 15-30 carbon atoms and R⁵ is an aliphatichydrocarbon group having from 15-30 carbon atoms, and from 50 to 0% byweight of other polymerizable monomer, and (c) from 10 to 70% by volumeof a binder auxiliary (II), providing the total of the powdery material,the polymer (I), and the binder auxiliary (II) accounts for 100% byvolume, wherein after said composition is subjected to injectionmolding, said polymer (I) and said binder auxiliary (II) are removablefrom said injection molded product, whereby the residual molded productcomprising said powdery material is sinterable to provide the desiredsintered powdery material, free of said polymer (I) and said binderauxiliary (II).
 2. The powder injection molding according to claim 1,wherein said powdery material capable of sintering is the powder of atleast one member selected from the group consisting of metals, ceramicsubstances, and cermets.
 3. The powder injection molding according toclaim 1, wherein an average particle diameter of said powdery materialcapable of sintering is in the range of from 0.1 to 20 μm.
 4. The powderinjection molding according to claim 1, wherein said binder auxiliary(II) is at least one member selected from the group consisting of abinding agent, a plasticizer, and a slip additive.
 5. The powderinjection molding composition according to claim 1, wherein the amountof said polymer (I) is in the range of from 10 to 50% by volume and theamount of said binder auxiliary (II) is in the range of from 10 to 50%by volume providing the total of said polymer (I) and said binderauxiliary (II) and said powdery material accounts for 100% by volume. 6.The powder injection molding composition according to claim 1, whereinR¹ is H, R² is an aliphatic hydrocarbon group from 15 to 30 carbonatoms,and B is ##STR10## in the formula (1) and R⁴ is H or an aliphatichydrocarbon group of from 15 to 30 carbon atoms and R⁵ is an aliphatichydrocarbon group of from 1 5 to 30 carbon atoms in the formula (2). 7.The powder injection molding composition according to claim 1, whereinsaid long side chain-containing monomer is a long side chain-containingvinyl monomer represented by the formula (1).
 8. The powder injectionmolding composition according to claim 7, wherein R¹ is H, R² is analiphatic hydrocarbon group of from 15 to 30 carbon atoms, and B is##STR11## in the formula (1).
 9. The powder injection moldingcomposition according to claim 1, wherein the polymer (I) obtained bypolymerizing a monomer component comprises 80 to 100% by weight of saidlong side chain-containing monomer and 20 to 0% by weight of said otherpolymerizable monomer.
 10. The powder injection molding compositionaccording to claim 1, wherein said powdery material is metals.